Semiconductor memory device for use in multi-chip package

ABSTRACT

Provides is a multi-chip package including a plurality of semiconductor memory devices. Each of semiconductor memory devices includes a register and a control circuit. The register is configured to store start sequence information representing start of execution of a refresh operation in the multi-chip package. The control circuit is configured to control start of the execution of the refresh operation in response to the start sequence information stored in the register. Since the start of the execution of the refresh operation is performed in sequence of respective semiconductor memory devices according to the start sequence information stored in the register, consumption of peak current may be reduced in a power saving mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35USC §119 to Korean Patent Application No. 10-2013-0152499, filed on Dec.9, 2013, the entirety of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Embodiments of the present disclosure relate to semiconductor memorydevices and, more particularly, to a semiconductor memory device forsuitable use in a multi-chip package where a plurality of semiconductormemory devices are integrated in a single package.

When a plurality of semiconductor chips constitute a multi-chip packagetogether with or independently of a processor, a portable deviceincluding the multi-chip package may be miniaturized or its operatingperformance may be enhanced.

With the advance in portable devices, semiconductor memory devices suchas DRAMs typically tend to be integrated in a multi-chip package such asa dual die package (hereinafter referred to as “DDP”) or a quad diepackage (hereinafter referred to as “QDP”), not in a single-chippackage.

A predetermined operation, e.g., refresh operation may be performed insemiconductor memory devices that are present in a multi-chip package.Peak current of the multi-chip package may increase when self-refreshoperations of the semiconductor memory devices are performed at the sametime.

In general, set makers of portable devices give preference to multi-chippackages including a low power or peak current consumption during aself-refresh operation.

SUMMARY OF THE INVENTION

The present disclosure provides a semiconductor memory device and amulti-chip package.

Embodiments of the disclosure provide a semiconductor memory devicewhich may include a register configured to store start sequenceinformation representing start of execution of a refresh operation in amulti-chip package; and a control circuit configured to control start ofthe execution of the refresh operation in response to the start sequenceinformation stored in the register. The control circuit may include arefresh control circuit configured to delay start of the execution ofthe self-refresh operation in response to the start sequenceinformation.

In exemplary embodiments, four semiconductor memory devices may bemounted on the multi-chip package. Each of the semiconductor memorydevices may store independent start sequence information in theregister.

In exemplary embodiments, the refresh operation may include aself-refresh operation executed according to a self-refresh signal.

In exemplary embodiments, the semiconductor memory device may be adynamic random access memory (DRAM).

In exemplary embodiments, the self-refresh operation may be executed ina standby operation mode.

In exemplary embodiments, the start sequence information may bepermanently stored in the register by programming electrical fuses(e-fuses).

In exemplary embodiments, the start sequence information may be storedin the register by applying a mode register set signal.

In exemplary embodiments, the refresh control circuit may include adelay adjuster configured to differentiate start of the execution of theself-refresh operation in response to a value of the start sequenceinformation.

In exemplary embodiments, the delay adjuster may internally include aplurality of delay units for delay adjustment.

Embodiments of the disclosure provide a multi-chip package which mayinclude a substrate; and a plurality of semiconductor memory chipsstacked on a top or bottom surface of the substrate. Each of thesemiconductor memory chips may include a register configured to storestart sequence information for initiating execution of a refreshoperation in the multi-chip package; and a control circuit configured todifferentially control start of execution of the refresh operationaccording to the start sequence information stored in the register.

In exemplary embodiments, the multi-chip package may be a quad-diepackage (QDP) or a dual die package (DDP).

In exemplary embodiments, the semiconductor memory is a dynamic randomaccess memory (DRAM), and the refresh operation may be an auto-refreshoperation or a self-refresh operation.

In exemplary embodiments, the start sequence information may be storedin the register by programming electrical fuses (e-fuses).

In exemplary embodiments, the start sequence information may be storedin the register by applying a mode register set signal during aninitialization operation of the multi-chip package.

In exemplary embodiments, the start sequence information may beinformation for reducing peak current of the multi-chip package.

Embodiments of the disclosure provide a method for a refresh operationof a multi-chip package including a plurality of semiconductor memorydevices each having different chip identification information. Themethod may include receiving a refresh command from an outside of themulti-chip package; and for each semiconductor memory device, performinga refresh operation based on the refresh command. The performing therefresh operation may start at different times for each semiconductormemory device in response to the respective chip identificationinformation.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate exemplaryembodiments of the disclosure and, together with the description, serveto explain principles of the disclosure. In the drawings:

FIG. 1 is a block diagram of a memory system according to exampleembodiments;

FIG. 2 is a configuration block diagram of a multi-chip package in FIG.1 according to example embodiments;

FIG. 3 is an exemplary partial block diagram of a semiconductor memorydevice, such as a memory chip such as shown in FIG. 2 according to oneembodiment;

FIG. 4 is another exemplary partial block diagram of a memory chip inFIG. 2 according to one embodiment;

FIG. 5 is an exemplary circuit configuration diagram of a refreshcontrol circuit in FIG. 3 or 4 according to one embodiment;

FIG. 6 is an exemplary circuit configuration diagram of a refresh periodsignal generator in FIG. 5 according to one embodiment;

FIG. 7 is an exemplary operation timing diagram in FIG. 5;

FIG. 8 is a self-refresh operation timing diagram applied to FIG. 2according to example embodiments;

FIG. 9 is an exemplary circuit block diagram of a semiconductor memorydevice connected to FIG. 5 according to one embodiment;

FIG. 10 is a flowchart illustrating a method for a refresh operation ofa multi-chip package in FIG. 1 according to example embodiments;

FIG. 11 illustrates a memory system including semiconductor memorydevices stacked each other through TSV according to certain embodiments;

FIG. 12 illustrates an electronic system according to certainembodiments;

FIG. 13 is a block diagram illustrating a computing device according tocertain embodiments;

FIG. 14 is a block diagram illustrating a smart phone according tocertain embodiments;

FIG. 15 is a block diagram illustrating a mobile system according tocertain embodiments;

FIG. 16 is a block diagram illustrating an optical I/O schema accordingto certain embodiments;

FIG. 17 is a block diagram illustrating a portable multimedia systemaccording to certain embodiments;

FIG. 18 is a block diagram illustrating a personal computer according tocertain embodiments;

FIG. 19 is an exemplary diagram illustrating stacking implementation ofthe multi-chip package in FIG. 2; and

FIG. 20 is a block diagram of a computing system according to certainembodiments.

DETAILED DESCRIPTION

Example embodiments of the present disclosure will now be described morefully through the following exemplary embodiments related to theaccompanying drawings. However, the disclosure is not limited to thefollowing embodiments but may be embodied in other forms.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. Similarly, it will also be understood that when an element isreferred to as being “on” another element, it can be directly on theother element, or intervening elements may also be present. In contrast,when an element is referred to as being “directly connected” or“directly coupled” to another element, there are no interveningelements. Other words used to describe relationships between elementsshould be interpreted in a like fashion (i.e., “between” versus“directly between,” “adjacent” versus “directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to limit the disclosure. As usedherein, the singular terms “a,” “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. Expressionssuch as “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

It will be also understood that although the terms first, second, thirdetc. may be used herein to describe various elements, these elementsshould not be limited by these terms. Unless indicated otherwise, theseterms are only used to distinguish one element from another element.Thus, a first element in some embodiments could be termed a secondelement in other embodiments without departing from the teachings of thepresent disclosure. Exemplary embodiments of aspects of the presentdisclosure explained and illustrated herein include their complementarycounterparts. The same reference numerals or the same referencedesignators denote the same elements throughout the specification.

Unless the context indicates otherwise, terms such as “same,” “planar,”or “coplanar,” as used herein when referring to orientation, layout,location, shapes, sizes, amounts, or other measures do not necessarilymean an exactly identical orientation, layout, location, shape, size,amount, or other measure, but are intended to encompass nearly identicalorientation, layout, location, shapes, sizes, amounts, or other measureswithin acceptable variations that may occur, for example, due tomanufacturing processes. The term “substantially” may be used herein toreflect this meaning.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present application, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Moreover, the same or like reference numerals in each of the drawingsrepresent the same or like components if possible. In some drawings, theconnection of elements and lines is just represented to effectivelyexplain technical content and may further include other elements orcircuit blocks.

Note that each embodiment that is herein explained and exemplified mayalso include its complementary embodiment and the details of basic dataaccess operations (including read and write operations), a pre-chargeoperation, a refresh operation, and an internal function circuit on aDRAM are not described in order not to make the subject matter of thedisclosure ambiguous.

FIG. 1 is a block diagram of a memory system according to exampleembodiments. As illustrated, the memory system includes a memorycontroller 100, a multi-chip package 200, and a power supplying circuit300.

The memory controller 100 transmits a command, an address, and data tothe multi-chip package 200 through a bus B1. The bus B1 also serves toapply data or a strobe signal output from the multi-chip package 200 tothe memory controller 100.

If the power supplying circuit 300 is mounted inside the memory system,the power supplying circuit 300 receives external power and converts theexternal power to an internal power of the memory system. The internalpower may be applied to the multi-chip package 200 through a line L1.The memory system in FIG. 1 is merely an exemplary configuration, andthe multi-chip package 200 may directly receive the external power.

The multi-chip package 200 may be implemented as, for example, a QDP ora DDP. In such a case, peak current may increase when self-refreshoperations are simultaneously performed on all chips.

The multi-chip package 200 may be mounted using various types ofpackages such as PoP (package on package), ball grid array (BGA), chipscale package (CSP), plastic leaded chip carrier (PLCC), plastic dualin-line package (PDIP), die in waffle pack, die in wafer form, chip onboard (COB), ceramic dual in-line package (CERDIP), plastic metric quadflat pack (MQFP), thin quad flat pack (TQFP), small outline (SOIC),shrink small outline package (SSOP), thin small outline (TSOP), thinquad flatpack (TQFP), system in package (SIP), multi chip package (MCP),wafer-level fabricated package (WFP) and wafer-level processed stackpackage (WSP).

Accordingly, in example embodiments, circuit blocks shown in FIG. 3 or 4are prepared in respective chips of the multi-chip package shown in FIG.2 to minimize or decrease peak current. The circuit blocks shown in FIG.3 or 4 allows respective chips to sequentially operate for decreasingpeak current during a predetermined operation such as a self-refreshoperation.

FIG. 2 is a configuration block diagram of the multi-chip package 200 inFIG. 1 according to example embodiments. As illustrated, the multi-chippackage 200 includes, for example, four chips which include a firstmemory chip 210 a, a second memory chip 210 b, a third memory chip 210c, and a fourth memory chip 210 d.

The first memory chip 210 a and the third memory chip 210 c may bemounted on an upper portion and a lower portion of a substrate,respectively.

In this specification, a single memory chip may mean a singlesemiconductor memory device having predetermined memory capacity, e.g.,1 gigabyte or 4 gigabytes. For example, a single memory chip may be apiece cut from a wafer. A single memory chip may be a die, that canconnect to other memory chips and/or a package substrate to form asemiconductor package.

A power line L13 of the first memory chip 210 a may receive powerthrough the line L1 in FIG. 1.

A power line L14 of the second memory chip 210 b may receive powerthrough the line L1 in FIG. 1, and a power line L12 of the third memorychip 210 c may receive power through the line L1 in FIG. 1. A power lineL11 of the fourth memory chip 210 d may receive power through the lineL1 in FIG. 1.

It will be understood that since the power lines L11 to L14 are commonlyconnected to the line L1, peak current may increase when the first tofourth memory chips 210 a to 210 d operate at the same time. Thus, insome embodiments, the first to fourth memory chips 210 a to 210 d havechip identification information, for example, start sequence informationin their registers. The start sequence information indicates a sequenceof executing a predetermined operation in a multi-chip package when theoperation is executed on a semiconductor memory device. For example,assuming that the first to fourth memory chips 210 a to 210 d haveinformation 1, information 2, information 3, and information 4respectively, a self-refresh operation starts from the first memory chip210 a. After predetermined time passes, the second memory chip 210 bstarts to execute a self-refresh operation. Thereafter, the third memorychip 210 c and the fourth memory chip 210 d sequentially start toexecute self-refresh operations. These self-refresh operations may besimultaneously terminated in the first to fourth memory chips 210 a to210 d. As such, although starts of self-refresh operations aresequentially done in units of respective chips to reduce a peak currentfrom increasing, terminations of the self-refresh operations may besimultaneously done in the multi-chip package.

Each of the first to fourth memory chips 210 a to 210 d may include aregister configured to store respective start sequence information. Eachof the first to fourth memory chips 210 a to 210 d may include a controlcircuit configured to control the start of operation execution accordingto the start sequence information stored in the register.

FIG. 3 is an exemplary partial block diagram of a semiconductor memorydevice, such as a memory chip such as shown in FIG. 2, according to oneembodiment.

Referring to FIG. 3, a command decoder 260, a refresh control circuit280, and a chip ID register 290 constitute some blocks of the memorychip.

The command decoder 260 decodes an applied command CMD. When the commandCMD is an auto-refresh command, the command decoder 260 may output anauto-refresh command AREF_CMD as a result of the decoding.

The chip ID register 290 may function as the register and store chipidentification information such as start sequence information. If thechip ID register 290 includes an electrical fuse (e-fuse) 292, the startsequence information may be permanently recorded by programming thee-fuse 292. For example, in case of a second chip in the multi-chippackage 200, the information (e.g., data) “01” may be stored byelectrically blowing the e-fuse 292. Since the information “01”corresponds to the start sequence information and may be used asinformation to delay the counting of a refresh operation, theinformation “01” may be described as a delay counting signal DC in thisspecification.

The refresh control circuit 280 receives the auto-refresh commandAREF_CMD and a clock enable signal CKE. The refresh control circuit 280also receives the delay counting signal DC, which is the start sequenceinformation, from the chip ID register 290.

In one embodiment, the refresh control circuit 280 generates an internalrefresh signal REFP and an internal address counting signal RCNTI[0:N]to control the execution of a refresh operation through circuit blocksshown in FIG. 5.

FIG. 4 is another exemplary partial block diagram of a memory chip inFIG. 2 according to one embodiment. The configuration in FIG. 4 isidentical to the configuration in FIG. 3, except that the chip IDregister 290 in FIG. 3 is replaced with a mode register 270.

It may be substantially impossible to change the delay counting signalDC that is the start sequence information stored in the chip ID register290 in FIG. 3. For example, since blowing of an e-fuse is nonvolatile,for example, register information programmed to “01” cannot be changedto “10”. Accordingly, a semiconductor memory chip having registerinformation stored as “01” in this example would always operatesecondarily. In contrast, the mode register 270 in FIG. 4 may havevariable register information to avoid fixed operation execution. Forexample, when a mode register set signal MRS is applied during power-upof the multi-chip package 200, the register information may varydepending on the applied mode register set signal MRS. Thus, anarbitrary memory chip operating primarily in an operation mode beforecurrent power-up may operate secondarily in a current operation mode.For example, a memory controller may change and apply the mode registerset signal MRS to a corresponding semiconductor memory chip.

A refresh control circuit 280 receives an auto-refresh command AREF_CMDand a clock enable signal CKE. The refresh control circuit 280 alsoreceives a delay counting signal, which is start sequence information,from the mode register 270.

In each power-up mode, the refresh control circuit 280 may variablygenerate an internal refresh signal REFP and an internal addresscounting signal RCNTI[0:N] to control the execution of a refreshoperation according to information of a delay counting signal DC.

In a DRAM, data is stored in the form of charge on a cell capacitor andthe stored charge may be lost due to leakage current or the like.Therefore, it is customary to perform a process of periodically sensingand amplifying stored data and rewriting the amplified data before thedata is completely erased. This process is typically called a refreshoperation.

A refresh operation may be classified into an auto-refresh operation anda self-refresh operation. The auto-refresh operation is performed byexternally applying an auto-refresh command AR at regular timeintervals. On the other hand, the self-refresh operation is one ofvarious operation modes of a semiconductor memory device and is used toreduce power consumption. In case of the self-refresh operation, aspecific command is not provided to a semiconductor memory device in anexternal chipset such as a memory controller. For example, in thisoperation mode, only a self-refresh entry condition is provided bychanging a logic state or the like of a clock enable signal. Then, thesemiconductor memory device performs self-refresh by itself depending onthe operation of an internal counter before reaching a self-refresh exitcondition. During a self-refresh operation performed in a low power mode(e.g., power saving mode), circuit blocks unassociated with aself-refresh operation such as an input buffer and a delay locked loop(DLL) are turned off to minimize power consumption. For example, in caseof an application (AP) of a mobile device, the specification prescribesthat output peak current is equal to or less than 20 mA in a low power(LP) mode.

FIG. 5 is an exemplary circuit configuration diagram of the refreshcontrol circuit 280 in FIG. 3 or 4 according to one embodiment. Asillustrated, the refresh control circuit 280 includes a mode controlcircuit 10, a refresh interval signal generator 20, a refresh periodsignal generator 30, an internal refresh signal generator 40, and aninternal address counting circuit 50.

The mode control circuit 10 receives a clock enable signal CKE and anauto-refresh command AREF_CMD to generate an internal auto-refreshsignal AREFP, a self-refresh entry signal SRFE_EN, and a self-refreshexit signal SREF_EXP. The clock enable signal CKE indicates whether aclock to synchronize driving of a semiconductor memory device is valid.Accordingly, when only the clock enable signal CKE is disabled, thesemiconductor memory device enters a power-down mode or a power savingmode to minimize its power consumption.

The refresh interval signal generator 20 receives the internalauto-refresh signal AREFP, the self-refresh entry signal SREF_EN, theself-refresh exit signal SREF_EXP, and the start sequence information(delay counting signal DC) to generate a self-refresh signal SREFnotifying a start of executing a self-refresh operation.

The refresh period signal generator 30 periodically outputs aperiod-pulse signal PL_FLG during the enabling of the self-refreshsignal SREF.

The internal refresh signal generator 40 enables an internal refreshsignal REFP in response to the internal auto-refresh signal AREFP andthe period-pulse signal PL_FLG. For example, the internal refresh signalREFP may control a start of enabling a word line or bit line senseamplifier of each of the semiconductor memory devices to reduce a peakcurrent.

The internal address counting circuit 50 increases a row address inunits of one bit and outputs the increased row address as an internaladdress RCNTI[0:N] in response to the internal refresh signal REFP. Assuch, for each semiconductor memory device, the internal addresscounting circuit 50 may start execution of an internal address countingoperation at different times.

FIG. 6 is an exemplary circuit configuration diagram of the refreshperiod signal generator 20 in FIG. 5 according to one embodiment. Asillustrated, the refresh period signal generator 20 includes a signalgenerator 22 to enable an output signal of the signal generator 22during the enabling of the self-refresh entry signal SREF_EN and theinternal auto-refresh signal AREFP and to disable an output signal ofthe signal generator 22 during the enabling of the self-refresh exitsignal SREF_EXP, a latch 24 to latch an output signal of the signalgenerator 22, and a delay adjuster 26 to delay the output signal of thesignal generator 22 according to the delay counting signal DC and tooutput the delayed output signal as a self-refresh signal SREF.

The delay adjuster 26 serves to differentiate a delay in start of theself-refresh operation by using the self-refresh signal SREF in responseto a value of the start sequence information (e.g., delay countingsignal DC).

The signal generator 22 outputs a logic ‘L’ level when both theself-refresh entry signal SREF_EN and the internal auto-refresh signalAREFP become a logic ‘H’ level. The latch 24 latches the output signalof a logic ‘L’ level of the signal generator 22. For example, the delayadjuster 26 allows the self-refresh signal SREF to be output afterpassing through only an inverter I1 when a value of the delay countingsignal DC is 00 and allows the self-refresh signal SREF to be outputafter passing through only three inverters I1, I2, and I3 when a valueof the delay counting signal DC is 01.

When the self-refresh signal SREF is output through odd inverters, theself-refresh signal SREF is enabled to a logic ‘H’ level. However, thisis merely exemplary and the self-refresh signal SREF may pass througheven inverters to obtain an output of logic ‘L’ level.

On the other hand, when the self-refresh exit signal SREF_EXP is enabledto a logic ‘L’ level, the signal generator 22 disables an output signalto a logic ‘H’ level. The latch 24 latches the output signal of thesignal generator 22, and the self-refresh signal SREF is disabled by thedelay adjuster 26.

In one embodiment, the refresh interval signal generator 20 enables theself-refresh signal SREF after the enabling of the self-refresh entrysignal SREF_EN and the internal auto-refresh signal AREFP. This enabledself-refresh signal is maintained before the self-refresh exit signalSREF_EXP is enabled. Afterwards, the self-refresh signal SREF isdisabled when the self-refresh exit signal SREF_EXP is enabled.

FIG. 7 is an exemplary operation timing diagram in FIG. 5. In FIG. 7,operation timing of generating the self-refresh execution signal SREF inFIG. 5 is exemplarily shown.

When a clock enable signal CKE transitions to a logic 1′ level while anauto-refresh command AREF_CMD is enabled, the mode control circuit 10enables the self-refresh entry signal SREF_EN. The refresh intervalsignal generator 20 enables the self-refresh execution signal SREF inresponse to the internal auto-refresh signal AREFP and the self-refreshentry signal SREF_EN. This enabling of the self-refresh execution signalSREF is maintained until self-refresh execution signals SREF1 to SREF4become low.

FIG. 8 is a self-refresh operation timing diagram applied to FIG. 2according to one embodiment. In FIG. 8, a self-refresh entry signalSREF_EN and self-refresh execution signals SREF1 to SREF4 are shown.

When the self-refresh entry signal SREF_EN is generated from the modecontrol circuit 10 in FIG. 5, the refresh interval signal generator 20may generate one of the self-refresh execution signals SREF1 to SREF4according to information of the delay counting signal DC.

Accordingly, as indicated by an arrow AR1, a self-refresh operation ofthe first memory chip 210 a in FIG. 2 may start at timing t1 and, asindicated by an arrow AR2, a self-refresh operation of the second memorychip 210 b in FIG. 2 may start at timing point t2 that is delayed by D1from the timing t1. In addition, as indicated by an arrow AR3, aself-refresh operation of the third memory chip 210 c in FIG. 3 maystart at timing t3 that is delayed by D2 from the timing t2 and, asindicated by an arrow AR4, a self-refresh operation of the fourth memorychip 210 d may start at timing t4 that is delayed by D3 from the timingt3. In one embodiment, all the self-refresh execution signals SREF1 toSREF4 may be disabled at the same time t5 based on enabling theself-refresh exit signal SREF_EXP.

Accordingly, since self-refresh operations are sequentially performed inunits of memory chips, a peak current value appearing on a line L1 maybe reduced as compared to a case where all memory chips start aself-refresh operation at the same time.

FIG. 9 is an exemplary circuit block diagram of a semiconductor memorydevice connected to FIG. 5 according to one embodiment. FIG. 9 shows aconnection configuration of row selection to refresh memory cells of amemory cell array 254.

A reference term IRADD indicates the internal address counting signalRCNTI[0:N], which is provided to a one-side input of a multiplexer 250.The multiplexer 250 selects one of the IRADD and an external row addressXRADD and outputs the selected one as a row address RADD. When theenabled internal refresh signal REFP is applied to the multiplexer 250as a selection signal, the multiplexer 250 outputs the IRADD as the rowaddress RADD.

A row selection circuit 252 decodes the row address RADD such that ahigh driving voltage Vin is applied to a selected word line. A selectedone of word lines WL1 to WLn of a memory cell array 254 is activated torefresh data stored in memory cells connected to the selected word line.

The row selection circuit 252 performs a row selection operation forexecuting a refresh operation in response to the internal refresh signalREFP. The row selection circuit 252 may include a row decoder and a wordline driver. For example, the selected word lines of each of thesemiconductor memory devices may be enabled at different times,respectively. Accordingly, a peak current of the multi-chip package canbe reduced.

A row decoder connected to the memory cell array 254 decodes a rowaddress to enable a selected one of a plurality of word lines.

A sense amplifier (e.g., a bit line sense amplifier) connected to a bitline intersecting the word line detects a potential appearing on a bitline of a selected memory cell to sense data stored in the selectedmemory cell. After data sensing is completed, the sensed data isrestored in a corresponding memory cell during a self-refresh operation.For example, a bit line sense amplifier may also be controlled by theinternal refresh signal REFP to differentiate start time of execution ofthe bit line sense amplifier operation. The bit line sense amplifiers ofeach of the semiconductor memory devices are enabled at different times,respectively. Accordingly, a peak current of the multi-chip package canbe reduced.

FIG. 10 is a flowchart illustrating a method 100 for a refresh operationof a multi-chip package in FIG. 1 according to example embodiments.Referring to FIG. 10, chip information for a plurality of semiconductordevices may be stored (step S110). For example, each of thesemiconductor memory devices may include chip identification informationsuch as ‘00’ to ‘11’. In one embodiment, the chip identificationinformation may be stored in a chip ID register (e.g., a fuse circuit)or a mode register of each semiconductor memory device as shown FIGS. 3and 4. For example, when the chip identification information is storedin a fuse circuit, the storing operation may be processed during amanufacturing of the semiconductor memory device. On the other hand,when the chip identification information is stored in a mode register,the storing operation may be processed when the multi-chip package isoperating (e.g., power-up). For example, the respective chipidentification information may be received from an outside of themulti-chip package and stored in the mode register of each of thesemiconductor memory devices.

In step S120, a refresh command is received at a multi-chip packageincluding a plurality of semiconductor memory devices (e.g., chips)stacked on each other. Next, when a refresh operation (e.g., aself-refresh operation) is performed based on the refresh command, therefresh operation may start at different times for each semiconductormemory device in response to the respective chip identificationinformation (step S130). In one embodiment, the self-refresh operationof each of the semiconductor memory devices may be finished at the sametime. The self-refresh operation of each of the semiconductor memorydevices may be controlled by a refresh control circuit of FIG. 5, whichdelays a start of the self-refresh operation in response to therespective chip identification information. The refresh operation ofeach of the semiconductor memory devices may include enabling a wordline or a bit line sense amplifier at different times for eachsemiconductor memory device.

FIG. 11 illustrates a memory system including semiconductor memorydevices stacked on each other through a through substrate via (e.g., athrough silicon via (TSV)) according to certain embodiments. Referringto FIG. 11, an interface chip 3010 is disposed at a lowermost layer andmemory chips 3100, 3200, 3300, and 3400 are disposed thereon. The memorychips 3100, 3200, 3300, and 3400 may include sensing and storagecircuits 3601, 3602, 3603, and 3604, respectively. A micro bump (uBump)(not shown) may connect between one chip and another chip. Therespective chips may be connected through TSVs 3500. For example, one ormore chips may be stacked.

In case of FIG. 11, the memory chips 3100, 3200, 3300, and 3400 may beimplemented using the multi-chip package 200 shown in FIG. 1. Since thememory chips 3100, 3200, 3300, and 3400 operate with their inherentdelays during a refresh operation, peak current of a multi-chip packagedecreases.

FIG. 12 illustrates an electronic system according to certainembodiments. As illustrated, an MRAM 3500 including a data read circuit3550, a central processing unit (CPU) 3150, and a user interface areconnected through a system bus 3250. The MRAM 3500 may be implementedusing a multi-chip package such as the multi-chip package 200 shown inFIG. 1.

If the electronic system is a portable electronic device, a separateinterface may be connected to an external communication device. Thecommunication device may be a digital versatile disc (DVD) player, acomputer, a set top box, a game player, a digital camcorder or the like.

A chip of the MRAM 3500 or a chip of the CPU 3150 may be packagedindependently or together as one of various types to be subsequentlyembedded. For example, a chip may be packaged by one of PoP (Package onPackage), Ball Grid Arrays (BGAs), Chip Scale Packages (CSPs), PlasticLeaded Chip Carrier (PLCC), Plastic Dual In-Line Package (PDIP), Die inWaffle Pack, Die in Wafer Form, Chip On Board (COB), Ceramic DualIn-Line Package (CERDIP), Plastic Metric Quad Flat Pack (MQFP), ThinQuad Flatpack (TQFP), Small Outline (SOIC), Shrink Small Outline Package(SSOP), Thin Small Outline (TSOP), Thin Quad Flatpack (TQFP), System InPackage (SIP), Multi Chip Package (MCP), Wafer-level Fabricated Package(WFP), and Wafer-Level Processed Stack Package (WSP).

In FIG. 12, a flash memory may be further employed in the bus 3250.However, various types of nonvolatile storages may be used withoutlimitation thereto.

The nonvolatile storage may store data information having various dataformats such as texts, graphics, and software codes.

Even in the case of FIG. 12, a chip of the MRAM 3500 may be implementedas a part of a multi-chip page. Thus, since an operation in apredetermined mode is performed with a delay equivalent to a delay setin a power saving mode, peak current consumed may be reduced orminimized.

FIG. 13 is a block diagram illustrating a computing device according tocertain embodiments. As illustrated, the computing device may include amemory system 4500 including a DRAM 4520 and a memory controller 4510.The computing device may include an information processing device, acomputer or the like. In some embodiments, the computing device mayinclude a memory system 4500 and a modem 4400, a CPU, a RAM 4200, and auser interface 4300 that are electrically connected to a system bus4250. Data processed by the CPU 4100 or externally input data may bestored in the memory system 4500.

The computing device may be applied to a solid state disk (SSD), acamera image sensor, and other application chipsets. In someembodiments, the memory system 4500 may be configured with an SSD. Inthis case, the computing device may stably and reliably large-capacitydata in the memory system 4500.

Since the DRAM 4520 constituting the memory system 4500 may beimplemented using a multi-chip package such as shown in FIG. 1, peakcurrent consumption characteristics of the computing device may beenhanced.

The memory controller 4510 may apply a command, an address, data orother control signals to the DRAM 4520 channel-independently.

The CPU 4100 functions as a host and controls the overall operation ofthe computing device.

A host interface between the CPU 4100 and the memory controller 4150 mayinclude various protocols for data exchange between a host and thememory controller 4500. In exemplary embodiments, memory controller 4510may be configured to communicate with a host or an external devicethrough one of various interface protocols such as USB (Universal SerialBus) protocol, MMC (Multimedia Card) protocol, PCI (Peripheral ComponentInterconnection) protocol, PCI-E (PCI-Express) protocol, ATA (AdvancedTechnology Attachment) protocol, SATA (Serial ATA) protocol, ESDI(Enhanced Small Disk Interface) protocol, and IDE (Integrated DriveElectronics) protocol.

The computing device shown in FIG. 13 may be applied as one of acomputer, an Ultra Mobile PC (UMPC), a digital picture player, a digitalvideo recorder, a digital video player, a storage constituting a datacenter, a device capable of transmitting/receiving data in an wirelessenvironment and various electronic devices constituting a home network,one of various electronic devices constituting a computer network, oneof various electronic devices constituting a telematics network, aradio-frequency identification (RFID) device, or one of variousconstituents constituting a computing system.

Even in the case of FIG. 13, the DRAM 4520 may function as a part of amulti-chip package and thus a predetermined operation may be performedat predetermined timing.

FIG. 14 is a block diagram illustrating a smart phone according tocertain embodiments. In FIG. 14, a block diagram of main parts of amobile phone such as a DRAM-incorporated smartphone is shown. Asillustrated, a smartphone may include an antenna (ATN) 501, an analogfront-end block (AFE) 503, analog-digital converter circuits (ADC1 andADC2) 505, digital-analog converter circuits (DAC1 and DAC2) 507, abaseband block (BBD) 509, a speaker (SPK) 521, a liquid crystal monitor(LCD) 523, a microphone (MIK) 525, and an input key (KEY) 527. Althoughomitted in this figure, an analog front-end block 503 is a circuit blockwhich includes an antenna switch, a bandpass filter, various amplifiers,a power amplifier, a phase-locked loop (PLL), a voltage controloscillator (VCO), a quadrature demodulator, and a quadrature modulatorand performs transmission and reception of radio waves. The basebandblock 509 may include a signal processing circuit (SGC) 511 and abaseband processor (BP) 513, and a DRAM 515.

The operation of the smartphone according to FIG. 14 will now bedescribed. When an image including voice and text information isreceived, a radio wave input from an antenna is input to theanalog-digital converter circuit (ADC1) 505 through the analog front-endblock (AFE) 503 and is subjected to waveform equalization andanalog-to-digital conversion. An output signal of the analog-digitalconverter circuit (ADC1) 505 is input to the signal processing circuit(SGC) 511 in the baseband block 509 to perform voice and imageprocessing. A voice signal is transmitted to the speaker 521 from thedigital-analog converter circuit (DAC2) 517, and an image signal istransmitted to the liquid crystal monitor 523.

When the voice signal is transmitted, a signal input from the microphone525 is input to the signal processing circuit (SGC) 511 through theanalog-digital converter circuit (ADC2) 519 to perform voice processing.An output of the signal processing circuit (SGC) 511 is transmitted tothe antenna 501 from the digital-analog converter circuit (DAC1) 507through the analog front-end block 503. When the text information istransmitted, a signal input from the input key 527 is transmitted to theantenna 501 through the baseband block 509, the digital-analog convertercircuit 507, and the analog front-end block (AFE) 503.

In FIG. 14, the DRAM 515 may be implemented using a multi-chip package,for example, the multi-chip package 200 shown in FIG. 1. In such a case,the DRAM 515 may access the baseband processor 513 through a firstchannel and access an application processor (not shown) through a secondchannel. As a result, a single memory chip may be shared by twoprocessors.

Although the DRAM 515 is mounted in FIG. 14, an MRAM is mounted insteadof the DRAM 515 in other cases.

Volatile semiconductor memory devices such as SRAM and DRAM lose theirstored data when their power supplies are interrupted.

In contrast, nonvolatile semiconductor memory devices such as magneticrandom access memory (MRAM) retain their stored data even when theirpower supplies are interrupted. Thus, nonvolatile semiconductor memorydevices are preferentially used to data when there is a desire toprevent data loss caused by power failure or power-off.

When a spin transfer torque magneto resistive random access memory(STT-MRAM) constitute a multi-chip package, decrease in peak current andadvantages of an MRAM may be added.

An STT-MRAM cell may include a magnetic tunnel junction (MTJ) elementand a selection transistor. The MTJ element may basically include apinned layer, a free layer, and a tunnel layer disposed therebetween. Amagnetization direction of the pinned layer is fixed, and amagnetization of the free layer may be identical to or revere to that ofthe pinned layer according to conditions.

FIG. 15 is a block diagram illustrating a mobile system according tocertain embodiments. As illustrated, the mobile system such as anotebook computer may include a microprocessing unit (MPU) 1100, adisplay 1400, an interface (I/F) unit 1300, a DRAM package 2000, and asold-state drive (SSD) 3000.

If the mobile system is a portable communication device, a transceiverand a modem to modulate/demodulate communication data andtransmit/receive the data may be connected to the interface unit 1300.

The MPU 1100 controls the overall operation of the mobile systemaccording to a predetermined program.

The DRAM package 2000 may be connected to the MPU 1100 through a systembus and function as a buffer memory or a mina memory of the MPU 1100.

Since the DRAM package 2000 may constitute a multi-chip package 200shown in FIG. 1, consumption of peak current may be reduced in a powersaving mode.

The flash memory 3000 may be a NOR-type or NAND-type flash memory.

The display 1400 may include a touch screen as a component of a liquidcrystal having backlight, a liquid crystal having an LED light source oran organic light emitting diode (OLED). The display 1400 may function asan output component to display images such as letters, numbers, andfigures in color.

While the mobile system has been mainly described with respect mobilecommunication devices, the mobile system may function as a smart card byadding or removing its components, if necessary.

The mobile system may connect a separate interface to an externalcommunication device. The communication device may be a digitalversatile disc (DVD) player, a computer, a set top box (STB), a gameplayer, a digital camcorder or the like.

Although not shown in the figure, it will be apparent to those skilledin the art that the mobile system may be further provided with anapplication chipset, a camera image processor (CIS), a mobile DRAM, andso forth.

Although FIG. 8 illustrates an example where a flash memory is employedin a mobile system, various types of nonvolatile storages may beemployed.

The nonvolatile storage may store data information having various dataformats such as texts, graphics, and software codes.

FIG. 16 is a block diagram illustrating an optical I/O schema accordingto certain embodiments. As illustrated, a memory system 30 adopting ahigh-speed optical I/O includes a chipset 40 that is a controllermounted on a printed circuit board (PCB) 31 and memory modules 50 and60. The memory modules 50 and 60 may be inserted into slots 35_1 and35_2 installed on the PCB 31, respectively. The memory module 50 mayinclude a connector 57, channel DRAM memories 55_1 to 55 _(—) n, anoptical I/O input part 51, and an optical I/O output part 53.

The optical I/O input part 51 may include a photoelectric conversiondevice for converting an applied optical signal into an electricalsignal, for instance, a photodiode. Thus, an electrical signal outputfrom the photoelectric conversion device is received to the memorymodule 50. The optical I/O output part 53 may include a conversiondevice for converting an electrical signal output from the memory module50 into an optical signal, for instance, a laser diode. If necessary,the optical I/O output part 53 may further include an optical modulatorfor modulating a signal output from a light source.

An optical cable 33 is in charge of an optical communication between theoptical I/O input part 51 of the memory module 50 and an opticaltransmission part 41_1 of the chipset 40. The optical communication mayhave a bandwidth of several tens of gigabits per second or more. Thememory module 50 may receive signals or data applied from signal lines37 and 39 of the chipset 40 through the connector 57 and may perform ahigh speed data communication with the chipset 40 through the opticalcable 33. Resistors Rtm installed in lines 37 and 39 are terminationresistors.

In even the case of the memory system 30 adopting an optical I/Ostructure, the channel DRAM memories 55_1 to 55 _(—) n may be mounted ina multi-chip package such as the multi-chip package 200 shown in FIG. 1.

Accordingly, the chipset 40 may independently perform a data readoperation and a data write operation for each channel.

In FIG. 16, the chipset 40 may include a concentration access detector210 to generate a concentration access detection signal when thefrequency of applying a frequently applied address is greater than apredetermined threshold value.

The chipset 40 may prevent or mitigate corruption of data retained bymemory cells in adjacent memory regions adjacent to a specific memoryregion when the concentration access detection signal is generated.

For example, when a specific wordline, a specific bitline or a specificmemory block of a volatile semiconductor memory such as DRAM isconcentrically accessed, memory cell data may be corrupted. That is,memory cells of adjacent wordlines adjacent to a specific wordline,adjacent bitlines adjacent to a specific bitline or adjacent memoryblock adjacent to a specific memory block may lose their retained datadue to concentric access of their retained data. Thus, there is a needto prevent or mitigate loss of cell data through elimination oravoidance of address concentration.

When channel DRAM memories 55_1 to 55 _(—) n of the memory modules 50and 60 are accessed in units of memory pages, columns or banks, theconcentration access detector 210 monitors access concentration.

If the memory system in FIG. 16 is an SSD, the channel DRAM memories55_1 to 55 _(—) n may be used as a user data buffer.

FIG. 17 is a block diagram illustrating a portable multimedia system 500according to certain embodiments. As illustrated, the portablemultimedia system 500 may include an AP 510, a memory device 520, astorage device 530, a communication module 540, a camera module 550, adisplay module 560, a touch panel module 570, and a power module 580.

The AP 510 may perform a data processing function.

In FIG. 17, the memory device 520 may include a multi-chip package suchas the multi-chip package 200 as shown in FIG. 1. Thus, since peakcurrent consumed by the memory device 520 may be reduced during theoperation of the portable multimedia system 500, performance of themultimedia system 500 may be powerful.

The communication module 540 connected to the AP 510 may function as amodem to transmit/receive communication data and modulate/demodulate thedata.

The storage device 530 may be implemented as a NOR-type or NAND-typeflash memory to store large-capacity information.

The display module 560 may include a touch screen as a component of aliquid crystal having backlight, a liquid crystal having an LED lightsource or an organic light emitting diode (OLED). The display module 560may function as an output component to display images such as letters,numbers, and figures in color.

The touch panel module 570 may provide a touch input to the AP 510solely or on the display module 560.

While the portable multimedia system 500 has been mainly described withrespect to mobile communication devices, the portable multimedia systemmay function as a smart card by adding or removing its components, ifnecessary.

The portable multimedia system may connect a separate interface to anexternal communication device. The communication device may be a digitalversatile disc (DVD) player, a computer, a set top box (STB), a gameplayer, a digital camcorder or the like.

The nonvolatile storage may store data information having various dataformats such as texts, graphics, and software codes.

The power module 580 performs power management of the portablemultimedia system. As a result, power saving of the portable multimediasystem is achieved when a PMIC scheme is applied into the portablemultimedia system.

The camera module 550 includes a camera image processor (CIS) and isconnected to the AP 510.

Although not shown in the figure, it will be apparent to those skilledin the art that the portable multimedia system may be further providedwith another application chipset, a mobile DRAM, and so forth.

FIG. 18 is a block diagram illustrating a personal computer 700according to certain embodiments. As illustrated, the personal computer700 may include a processor 720, a chipset 722, a data network 725, abridge 735, a display 740, a nonvolatile storage 760, a DRAM 770, akeyboard 736, a microphone 737, a touch unit 738, and a pointing device739.

In FIG. 18, the DRAM 770 may function as an element in a multi-chippackage such as the multi-chip package 200 as shown in FIG. 1. Thus,peak current consumed by the DRAM 770 may be reduced during theoperation of the personal computer 700.

The chipset 722 may apply a command, an address, data or other controlsignals to the DRAM 770.

The processor 720 functions as a host and controls the overall operationof the personal computer 700.

A host interface between the processor 720 between the processor 720 andthe chipset 722 includes various protocols for performing datacommunication.

The nonvolatile storage 760 may be implemented with an electricallyerasable programmable read-only memory (EEPROM), a flash memory, amagnetic random access memory (MRAM), a spin-transfer torque MRAM, aconductive bridging RAM (CBRAM), a ferroelectric RAM (FeRAM), a phasechange RAM (PRAM) which is also called an ovonic unified memory (OUM), aresistive RAM (RRAM or ReRAM), a nanotube RRAM, a polymer RAM (PoRAM), anano floating gate memory (NFGM), a holographic memory, a molecularelectronics memory device or an insulator resistance change memory.

The personal computer shown in FIG. 18 may be applied to one of an ultramobile PC (UMPC), a workstation, a net-book, a personal digitalassistant (PDA), a web tablet, a wireless phone, a mobile phone, a smartphone, an e-book, a portable multimedia player (PMP), a portable gamedevice, a navigation device, a black box, a digital camera, a3-dimensional television, a digital audio recorder, a digital audioplayer, a digital picture recorder, a digital picture player, a digitalvideo recorder, a digital video player, a device capable oftransmitting/receiving data in an wireless environment and variouselectronic devices constituting a home network, one of variouselectronic devices constituting a computer network, one of variouselectronic devices constituting a telematics network, a radio-frequencyidentification (RFID) device, or one of various constituentsconstituting a computing system.

FIG. 19 is an exemplary diagram illustrating stacking implementation ofthe multi-chip package 200 in FIG. 2.

In FIG. 19, a stacked surface of the multi-chip package is shown. Anexample shown in FIG. 19 is a quad-die package (QDP) where foursemiconductor chips 210 a, 210 b, 210 c, and 210 d stacked on a singlepackage substrate 205. In particular, there is shown a structure wheretwo semiconductor chips are stacked on both surfaces of the packagesubstrate 205, respectively. The package substrate 205 may be a printedcircuit board (PCB) or a lead frame substrate.

More specifically, the two semiconductor chips 210 a and 210 b arestacked on one surface of the package substrate 205, and the other twosemiconductor chips 210 c and 210 d are stacked on the other surfacethereof. As shown in the figure, these semiconductor chips 210 a, 210 b,210 c, and 210 d have the same size. For example, these semiconductorchips 210 a, 210 b, 210 c, and 210 may be the same products.

As shown in the figure, lower semiconductor chips 210 a and 210 c arebonded to both surfaces of the package substrate 205 by adhesive layers215 a and 215 c. Upper semiconductor chips 210 b and 210 d are spacedapart from the lower semiconductor chips 215 a and 215 c by spacer tapes230 a and 230 c, respectively. Adhesive layers 215 b and 215 d areattached to lower ends of the upper semiconductor chips 210 b and 210 dto be bonded to the spacer tapes 230 a and 230 c, respectively. Curingparts 215 a′, 215 b′, 215 c′, and 215 d′ are provided at portions ofedges of the adhesive layers 215 a, 215 b, 215 c, and 215 d bonded tolower ends of the four semiconductor chips 210 a, 210 b, 210 c, and 210d, respectively.

Conductive wires 220 a, 220 b, 220 c, and 220 d are connected to upperportions of the four semiconductor chips 210 a, 210 b, 210 c, and 210 dfrom an upper portion of the package substrate 205, respectively.

FIG. 20 is a block diagram of a computing system according to certainembodiments.

In FIG. 20, a computing system 1400 including a multi-chip package isshown. The computing system 1400 may include a microprocessor 1410, auser interface 1420, a modem 1460 such as a baseband chipset, a memorycontroller 1440, and a flash memory device 1450, which are electricallyconnected to a bus 1401. The flash memory device 1450 may include amulti-chip package shown in FIG. 1.

The flash memory device 1450 is connected to the microprocessor 1410through the memory controller 1440.

If the computing system 1400 is a mobile system, a battery 1430 may beadditionally provided to supply an operating voltage of the computingsystem 1400. Although not shown in the figure, it will be apparent tothose skilled in the art that the computing system 1400 may be furtherprovided with an application chipset, a camera image processor (CIS), amobile DRAM, and so forth.

The memory controller 1440 and the flash memory device 1450 mayconstitute, for example, a solid state drive/disk (SSD) that uses anonvolatile memory to store data. The memory controller 1440 and theflash memory device 1450 may be mounted on a single package.

Although the disclosure has been mainly described with respect to, forexample, a QDP-type multi-chip package, the detailed implementation ofoperations may be made different by changing, adding, or removing thecircuit configuration or arrangement in the drawings without departingfrom the technical spirit of the present disclosure in other cases.

In addition, although the disclosure has been mainly described withrespect to a semiconductor memory device such as DRAM, the disclosure isnot limited thereto and may be applied to other semiconductor memorydevices.

According to the above-described embodiments, peak current consumedduring a predetermined operation such as a self-refresh operation in amulti-chip package can be minimized or reduced.

While the disclosure has been particularly shown and described withreference to exemplary embodiments thereof, it will be apparent to thoseof ordinary skill in the art that various changes in form and detail maybe made therein without departing from the spirit and scope of thedisclosure, which is defined by the following claims.

What is claimed is:
 1. A method for a refresh operation of a multi-chippackage including a plurality of semiconductor memory devices eachhaving different chip identification information, the method comprising:receiving a refresh command from an outside of the multi-chip package;and for each semiconductor memory device, performing a refresh operationbased on the refresh command, wherein performing the refresh operationstarts at different times for each semiconductor memory device inresponse to the respective chip identification information, and whereinthe respective chip identification information is received from anoutside of the multi-chip package, and the respective chipidentification information is stored in a mode register or in a fusecircuit of each of the semiconductor memory devices.
 2. The method ofclaim 1, wherein performing the refresh operation is a self-refreshoperation.
 3. The method of claim 2, wherein performing the self-refreshoperation of each of the semiconductor memory devices is finished at thesame time.
 4. The method of claim 3, wherein performing the self-refreshoperation of each of the semiconductor memory devices is controlled by arefresh control circuit configured to delay a start of the self-refreshoperation in response to the respective chip identification information.5. The method of claim 1, wherein performing the refresh operationincludes enabling a word line or a bit line sense amplifier at differenttimes for each semiconductor memory device.
 6. A semiconductor memorydevice comprising: a register configured to store start sequenceinformation representing start of execution of a refresh operation in amulti-chip package; and a control circuit configured to control start ofthe execution of the refresh operation in response to the start sequenceinformation stored in the register, wherein the control circuit includesa refresh control circuit configured to delay start of the execution ofthe refresh operation in response to the start sequence information, andwherein the start sequence information is stored in the register byprogramming electrical fuses (e-fuses) or by applying a mode registerset signal.
 7. The semiconductor memory device of claim 6, wherein themulti-chip package includes a plurality of semiconductor memory devicesstacked on each other, and wherein each of the semiconductor memorydevices stores independent start sequence information in the register.8. The semiconductor memory device of claim 7, wherein the refreshcontrol circuit is configured to delay differently for differentsemiconductor memory devices based on the independent start sequenceinformation.
 9. The semiconductor memory device of claim 6, wherein therefresh operation includes a self-refresh operation.
 10. Thesemiconductor memory device of claim 6, wherein the semiconductor memorydevice is a dynamic random access memory (DRAM).
 11. The semiconductormemory device of claim 6, wherein the refresh control circuit includes adelay adjuster configured to differentiate start of the execution of therefresh operation in response to a value of the start sequenceinformation.
 12. The semiconductor memory device of claim 11, whereinthe delay adjuster internally includes a plurality of delay units fordelay adjustment.
 13. A multi-chip package comprising: a substrate; anda plurality of semiconductor memory chips stacked on a top or bottomsurface of the substrate, wherein each of the semiconductor memory chipscomprises: a register configured to store start sequence information forinitiating execution of a refresh operation in the multi-chip package;and a control circuit configured to differentially control start ofexecution of the refresh operation according to the start sequenceinformation stored in the register, wherein the start sequenceinformation is stored in the register by programming electrical fuses orby applying a mode register set signal during an initializationoperation of the multi-chip package.
 14. The multi-chip package of claim13, wherein the multi-chip package is a dual die package (DDP) or aquad-die package (QDP).
 15. The multi-chip package of claim 13, whereinthe semiconductor memory is a dynamic random access memory (DRAM), andthe refresh operation is an auto-refresh operation or a self-refreshoperation.
 16. The multi-chip package of claim 13, wherein a peakcurrent of the multi-chip package that occurs during the refreshoperation is reduced by using the start sequence information.